Influence of Physical Activity during Pregnancy on Type and Duration of Delivery, and Epidural Use: Systematic Review and Meta-Analysis

Cesarean delivery may increase the need for anesthesia administration, thereby causing potential risks to both maternal and fetal health. This article aimed to investigate the effect of physical activity during pregnancy on the type of delivery, the duration of labor, and the use of epidurals (registration No.: CRD42022370646). Furthermore, 57 RCTs (n = 15301) were included showing that physical activity could decrease the risk of cesarean section (z = 3.22, p = 0.001; RR = 0.87, 95% CI = 0.79, 0.95, I2 = 37%, Pheterogeneity = 0.004), and 32 RCTs (n = 9468) showed significant decreases in instrumental delivery through performing physical activity (z = 3.48, p < 0.001; RR = 0.84, 95% CI = 0.76, 0.93, I2 = 0%, Pheterogeneity = 0.63). A significant decrease in the 15 RCTs’ (n = 4797) duration of first stage labor was found in physically active pregnant women (z = 2.09, p = 0.04; MD = −62.26, 95% CI = −120.66, −3.85, I2 = 93%, Pheterogeneity < 0.001) compared to those not active. Prenatal physical activity could decrease the risk of cesarean section and instrumental delivery and the duration of first stage labor.


Introduction
Childbirth is a complex process that can have significant implications for the health of both mother and infant. Spontaneous delivery without the need for intervention such as instrumental delivery or cesarean section is recommended [1,2]. However, the World Health Organization (WHO) has stated that the global caesarean section rate has risen from around 7% in 1990 to 21% today. By 2030, it is projected that the caesarean section rate will reach 63% in East Asia, followed by Latin America and the Caribbean (54%), Western Asia (50%), North Africa (48%), Southern Europe (47%), and Australia and New Zealand (45%) [3]. Compared to vaginal delivery, cesarean delivery increases the risk of adverse outcomes for both mother and infant, delays recovery duration, and thus incurs higher medical costs [4]. However, vaginal delivery may also lead to an increase in acute and chronic maternal morbidity [5].
The most common indication for cesarean section is slow progress of labor leading to delayed delivery and maternal fatigue. Prolonged labor can lead to various deleterious consequences for the well-being and health of both the mother and the fetus. For the mother, these include fatigue and physical exhaustion, increased risk of infection, vaginal or perineal injury, and psychological stress. For the fetus, there may be risks of oxygen deprivation, distress, and injury, which can affect the functioning of the brain and other organs [6]. Then, limiting prolonged duration of labor is important. The second stage

Study Selection and Data Extraction
Only randomized controlled trials (RCTs) were selected. Articles published between 2010 and 2023, written in English and Spanish were considered for the search. Reference lists of selected studies, as well as of systematic reviews previously published on the same topic, were retrieved to ensure studies of interest were not missed by the electronic keyword search.
To ensure compliance with the inclusion criteria, two reviewers conducted an independent screening of the titles and abstracts. The abstracts that met the initial screening were then retained for full text revision. The full texts were also revised by two independent reviewers to identify outcomes of interest for data extraction. For studies where one reviewer recommended exclusion and the other inclusion, both reviewers tried to reach a consensus to make a final decision for exclusion or inclusion. In situations of absolute discrepancy, a third reviewer provided their expert opinion on whether the study should be included or excluded.
In cases where a study had multiple publications, the most recent or comprehensive publications was chosen as the primary source. However, relevant data from all the publications were extracted to ensure that no valuable information was overlooked.
Data extraction tables were created in an Excel sheet. One researcher extracted the data and then, data extraction was independently verified by a content expert to facilitate further analysis.
Extracted data were study characteristics (i.e., author last name, year, and country), total sample size and sample size per study group, intervention (type of quantifiable physical activity: frequency, intensity, type and duration of physical activity, duration of the intervention, adherence to the intervention, and supervised or unsupervised physical activity), and primary and secondary outcomes.

Quality of Evidence and Risk of Bias Assessments
To evaluate the certainty of evidence for each study design and outcome, the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework was used. This framework provides a standardized and comprehensive approach to assess the certainty of the evidence across multiple studies [17].
To evaluate the risk of bias of RCTs, the Cochrane Handbook was utilized. The potential sources of bias evaluated are: selection bias (inadequate randomization procedures), performances bias (compliance with the intervention), detection bias (flawed outcome measurement), attrition bias (incomplete follow-up and high loss to follow-up), and reporting bias (selective or incomplete outcome reporting) [18].

Statistical Analysis
Statistical analyses were performed with Review Manager software (RevMan, version 5.4). Dichotomous outcomes (i.e., cesarean delivery, instrumental delivery, and the use of epidural anesthesia) were expressed as categorical variable (Yes/No). The number of events in the intervention and control group were recorded and relative risks (RR) and odds ratio (OR) were calculated [19]. For continuous outcomes (duration of first, second, and third stage of labor), mean differences (MD) were calculated [20].
To establish the compensated average in both dichotomous and continuous analyses, a weight system was used that considered the sample size per groups and generally, contributed by each study. A random effects model was used for all analysis. Meta-analyses were performed separately by study design and significance was set at p-value < 0.05. To assess the variation in study results between studies (i.e., the degree of heterogeneity), the I 2 statistic was calculated. The I 2 statistic was interpreted using established thresholds: low heterogeneity-<25%, moderate heterogeneity-25% to 75%, and high heterogeneity->75%. In the cases of high heterogeneity, post hoc subgroup analyses were conducted to further explore heterogeneity. In this study we found high heterogeneity with duration of first, second, and third stage labor; therefore, we divided the articles of mentioned analyses into different subgroups according to the age of participants (age ≥ 30 years, 25-30 years, and <25 years).

Results
A total of 60 RCT studies met the inclusion criteria, involving 15,968 pregnant women across 20 countries after the search process that is shown in Figure 1.
Among all of the interventions, 33 included only supervised physical activity, 12 included a combination of supervised and unsupervised physical activity, and 15 included only unsupervised physical activity. Studies varied in frequency of exercise from 1 to 7 days per week, exercise intensity was low to moderate, and the duration of exercise sessions varied between 10 and 75 min. These interventions were carried out during the first, second, or third trimesters, and lasted from 3 to 30 weeks. The type of exercise included walking, stationary cycling, water aerobics, swimming, resistance training, stretching, Pilates, yoga, pelvic floor muscle training, or a combination of various exercise types (Table 1).

Certainty of Evidence and Risk of Bias
Collectively, the certainty of evidence was high. In some situations, blinding of participants to the group (intervention or control group) was not feasible, and it is typically impossible to achieve due to the intervention characteristics (physical activity intervention), resulting in unclear or high risk of bias (performance bias) depending on how it was recorded. Other sources of bias found in some cases were the impossibility to find the article protocol published (to compare the planned and measured outcomes), but also not reporting (or being uncertainly defined) the randomization process. Overall, the majority of the studies presented low risk of bias within the five types of bias assessed. Risk of bias analysis is reported in Figure 2.
x FOR PEER REVIEW 5 of 21 Among all of the interventions, 33 included only supervised physical activity, 12 included a combination of supervised and unsupervised physical activity, and 15 included only unsupervised physical activity. Studies varied in frequency of exercise from 1 to 7 days per week, exercise intensity was low to moderate, and the duration of exercise sessions varied between 10 and 75 min. These interventions were carried out during the first, second, or third trimesters, and lasted from 3 to 30 weeks. The type of exercise included walking, stationary cycling, water aerobics, swimming, resistance training, stretching, Pilates, yoga, pelvic floor muscle training, or a combination of various exercise types (Table  1).   tion), resulting in unclear or high risk of bias (performance bias) depending on how it w recorded. Other sources of bias found in some cases were the impossibility to find article protocol published (to compare the planned and measured outcomes), but also reporting (or being uncertainly defined) the randomization process. Overall, the major of the studies presented low risk of bias within the five types of bias assessed. Risk of b analysis is reported in Figure 2.

Effect of Prenatal Physical Activity on Cesarean Delivery
Overall, there was high certainty of evidence from 57 RCTs (n = 15,301) [9,22-39,4 43,45-79] regarding the effect of prenatal physical activity on cesarean section. A sign cant decrease in the risk of cesarean deliveries was found with prenatal physical activ compared to no physical activity (z = 3.22, p = 0.001; RR = 0.87, 95% CI = 0.79, 0.95, I 2 = 37 Pheterogeneity = 0.004) as shown in Figure 3.

Effect of Physical Activity during Pregnancy on Duration of the Third Stage of Labor
Eight RCTs were retrieved and analyzed in this analysis (n = 3443) [29,36,38,57,58,65,69,71]. No statistical differences (Figure 7) were observed overall between groups regarding duration of the third stage of labor (z = 1.07, p = 0.29; MD = −0.38, 95% CI = −1.09, 0.32, I 2 = 75%, Pheterogeneity < 0.001). It was necessary to split the studies into subgroups due to high heterogeneity present in the general analysis. In the first subgroup no statistical differences were found between study groups (z = 0. 71

Discussion
In this systematic review, 60 RCTs were included, and there was high certainty of evidence showing that prenatal physical activity could decrease the risk of cesarean delivery by 13% and the risk of instrumental delivery by 16%. We also found that prenatal physical activity was associated with 62.26 min of reduction in the duration of first stage labor.
A review developed by Domenjoz et al. [11] with 16 articles found that women performing exercise during pregnancy had a significant lower risk of cesarean delivery compared to those who did not, and another article published by Wang et al. [12] with 13 RCTs showed that women who exercise during pregnancy had a significantly higher incidence of vaginal delivery than non-physically active women. Furthermore, Davenport et al. [10], in their review published in 2019 with 20 articles analyzed, found that engaging in a prenatal exercise program was associated with a 24% reduction in the likelihood of instrumental delivery. Our systematic review and meta-analysis examined the relationship between physical activity during pregnancy and type of delivery, showing the same conclusions as previously published articles.  [21,29,35,40,42,48,49,51,55,62,64,66,79].

Discussion
In this systematic review, 60 RCTs were included, and there was high certainty of evidence showing that prenatal physical activity could decrease the risk of cesarean delivery by 13% and the risk of instrumental delivery by 16%. We also found that prenatal physical activity was associated with 62.26 min of reduction in the duration of first stage labor.
A review developed by Domenjoz et al. [11] with 16 articles found that women performing exercise during pregnancy had a significant lower risk of cesarean delivery compared to those who did not, and another article published by Wang et al. [12] with 13 RCTs showed that women who exercise during pregnancy had a significantly higher incidence of vaginal delivery than non-physically active women. Furthermore, Davenport et al. [10], in their review published in 2019 with 20 articles analyzed, found that engaging in a prenatal exercise program was associated with a 24% reduction in the likelihood of instrumental delivery. Our systematic review and meta-analysis examined the relationship between physical activity during pregnancy and type of delivery, showing the same conclusions as previously published articles.
Physical activity has been shown to reduce the risk of several pregnancy complications that are often associated with a higher likelihood of cesarean section and instrumental delivery, for example, physical activity during pregnancy has been linked to a lower risk of gestational diabetes mellitus, excessive gestational weight gain, and macrosomia [80,81]. Elsewhere, labor duration is another factor that may contribute to the association between physical activity and decreased risk of cesarean section and instrumental delivery. Regular physical activity during pregnancy has been shown to improve overall fitness, cardiovascular health, and muscle strength [82], which could potentially enhance the efficiency and progress of labor. Shorter labor duration is generally associated with a reduced need for medical intervention, including cesarean section and instrumental delivery. The majority of studies suggest that engaging in regular physical activity during pregnancy can be beneficial for reducing cesarean sections and instrumental deliveries. Consequently, it is necessary that pregnant individuals maintain an active lifestyle throughout their pregnancy.
Our results showed a significant decrease in the duration of first stage labor in the physical activity group compared with the control group. We did not find an association between physical activity during pregnancy and duration of second and third stage labor. Despite the high heterogeneity obtained and after dividing the articles in these three analyses into different subgroups, high heterogeneity was still reported in the first stage of labor meta-analysis (I 2 = 97%). However, due to the low number of articles and the impossibility to split the articles into other subgroups based on other factors, the research team opted to report the current analysis.
A previously published review [12] found that exercise during pregnancy had no significant influence on first and second stages of labor. Interestingly, a recent review [13] showed that exercise significantly reduced the duration of the second stage of labor, but it did not reduce the first stage of labor, which is contrary to the conclusion drawn from our study. This discrepancy in results between our study and this previous meta-analysis may be attributed to several factors such as differences in study design, inclusion criteria, sample size, or specific characteristics of the populations studied. Regarding the potential link between physical activity and the duration of labor, it is important to note that the first stage of labor is often associated with increased interventions and potential complications. The second stage of labor, although shorter in duration, is crucial for the actual delivery of the baby. The third stage of labor involves the delivery of placenta and is typically shorter compared to the previous stages [83]. Therefore, further research in needed to better understand the potential relationship between physical activity during pregnancy and the different stages of labor.
Our study did not find that prenatal physical activity significantly reducing the need for epidural use during labor. However, it is important to consider the potential advantage of reducing epidural use, such as minimizing medical interventions, promoting a more active and engaged birthing experience, and potentially reducing associated risks or side effects. Further research is essential to better understand the underlying mechanisms and causative factors contributing to this association. Factors such as improved pain tolerance, increased endurance, or enhanced overall fitness may play a role in reducing the need for epidurals among physically activity pregnant women. More researches are needed to better understand the potential importance of incorporating physical activity as part of prenatal care to optimize outcomes and potentially reduce the reliance on epidurals during childbirth.

Limitations and Strengths
Strengths of this article include the selection and review of both English and Spanish articles expanding the scope of our search in comparison to previous reviews that were restricting to one language, and the inclusion specifically of randomized controlled trials allowing for assessment of the features of physical activity interventions that may not be captured through observational studies (e.g., frequency and type of activity) and are deemed to provide more high certainty of evidence. However, these results should be interpreted with caution in lieu of the inclusion of studies deemed of low quality as well as heterogeneity in the contents of the included interventions. Limitations of this review were the difficulty of obtaining data due to the discrepancies at the moment of reporting data from these studies. This limitation precluded the chance of performing a meta-analysis of the total duration of gestation but also to assess epidural use through a quantitative measure. Other limitations were the high heterogeneity reported in some analyses and the shortage of published articles regarding outcomes of interest as duration of the second stage of delivery. In fact, analyzed articles did not clearly report definitions of stages, possibly increasing variability of analyzed articles per analysis. Division of articles was necessary in three meta-analyses, but due to some retrieved scientific literature not reporting all participant sociodemographic characteristics, it was opted to split articles according to maternal age. Future research should aim to further extrapolate findings based on intensity of the intervention, and types of physical activity.

Conclusions
This review identified that prenatal physical activity could reduce the risk for cesarean section, instrumental delivery, and decrease the duration of the first stage of labor.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.